Serialiser_Engine: Fix ToJson for null Name property

[FraserGreenroyd]

Issues addressed by this PR

Fixes #2938

Test files

{
	Name: null
}

Try converting this JSON string FromJson and then immediately ToJson on main and then on this PR. You should find it throws an error on main but this branch will continue.

Changelog

Additional comments

[FraserGreenroyd]

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[FraserGreenroyd]

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[FraserGreenroyd]

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[adecler]

Tested on the example provided and can this PR fixes the issue.
Code change makes sense.

[FraserGreenroyd]

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